The invention relates to a device for the cyclic rearrangement of a pile of rectangular or square sheets, or a so-called "picture-changer".
Picture changers are known from U.S. patent specification Nos. 4,238,898, 4,238,899, 4,241,528, 4,241,529, 4,245,417, 4,259,802 and 4,376,348. These specifications are all based on the principle that a pile of pictures, especially photographic prints, is held by two frame parts that are movable relative to one another, one of which may have a viewing window. During each complete cycle of movement of the frame parts, that is, pulling them fully away from each other and sliding them fully back together again, one picture is removed from one end of the pile and returned to the other end of the pile again. The picture changers have the following components for this:
A feeding means feeds pictures to a separating means; the separating means detaches an individual picture from the pile; a retaining means holds the individual picture separated from the pile in one of the frame parts whilst the remainder of the pile is held in the other frame part; a guide means guides the separated individual picture such that it goes onto the other end of the remainder of the pile.
One difficult problem associated with picture changers is that in some circumstances very high forces are needed in order for two sheets that are clinging together to be separated from one another. Provided that these are relatively thick sheets, for instance cards, it is possible to engage the edge that is at the rear in the direction of movement of the individual sheet with a strong hook and to "push" the sheet without, on the one hand, the hook slipping off or, on the other hand, a plurality of sheets being transported with it. As soon as thinner sheets are involved, however, this becomes problematic. A hook bent at 90.degree. can in fact slip off an obliquely cut sheet edge and so that this edge is sufficiently straight for it to be gripped by such a hook the entire pile has to be flattened out by applying considerable pressure. The pressure applied for this purpose in turn multiplies the difficulties, because the sheets, which by nature tend to cling together, whether because of static charge in a dry atmosphere or because of sticking in a humid atmosphere, only cling together that much more tightly. Even if this were acceptable, however, such a "changer" operating with a strong spring bias would be awkward to manipulate. This difficulty occurs especially in a case of an application which were it not for this difficulty would be a preferred application, that is the application of picture-changers to photographic prints. Photographic prints are only approximately 0.2 mm thick, and a changer is intended to function both with a pile of, for example, 30 or more photographs, and with only a few photographs, in an extreme case two photographs.
It is the aim of the invention to design a picture changer in such a manner that cyclic rearrangement is possible even where sheets with unpredictably curled edges clinging firmly together are involved, without a very considerable pressure having to be exerted on the pile in the direction of its thickness.